Motion search precision and VHQ mode.

[Killgore]

Hi!

Does it make sense to set VHQ higher than 1 (or even 0) if motion search precision isn?t set to its maximum (6)? Because, if I understand it correctly, VHQ at these higher levels does something similar to MSP.
And I have the same question concerning chroma motion. Should I rather set MSP to 5 with chroma motion or 6 without it (encoding time is similar)?

TIA :)

[Prettz]

Enabling chroma motion seems like it would be a much different case from enabling VHQ, since it means that you are now including chroma motion in your slightly-lower-precision motion searching. I would guess that, in the most general sense, enabling chroma motion in this case could certainly make sense.

[Didée]

That question is indeed somewhat interesting.

What happens if you use e.g. ME=4 + VHQ1~4 ?

ME=4 does NO m4v search at all, but vhq will do 'additional' search ...

And it does do something:

The results of

1. ME=4 + VHQ=0
2. ME=4 + VHQ=1|..|4
3. ME=5|6 + VHQ=0
4. ME=5|6 + VHQ=1|..|4

are all different.

Now, I don't understand a single line of xvid's code - but let me do some wild guessing out of the blue. /syskin starts shuddering once again
Could the following be:

- When using VHQ with ME=5|6, then VHQ is basing its additional search on the m4v vectors coming out of the normal ME
- When using VHQ with ME=4, then VHQ is basing its search on the "single macroblock vectors" from normal ME (perhaps interpolating initial m4v's out of the macroblock vectors)

Perhaps these are totally wrong assumptions -- but if not, then suddenly the "floating wall" problem springs into my mind ...

- Didée

[mf]

Always use MSP at max and VHQ at max. The problems with VHQ>1 have long since been fixed.

[sysKin]

Originally posted by Didée
That question is indeed somewhat interesting.I agree. It would be interesting to find out what is the exact order of options which increase quality and decrease speed. If I'm bored enough, I might try different options and mark the results on time/psnr plot. What fun.

What happens if you use e.g. ME=4 + VHQ1~4 ?
ME=4 does NO m4v search at all, but vhq will do 'additional' search ...Additional search will ignore m4v result. It's a waste :) but the library will listen to user's request and if m4v is disabled (I think it's a requirement of simple profile level 0, maybe even level 1), encoder will not use m4v.
Originally posted by Killgore
Does it make sense to set VHQ higher than 1 (or even 0) if motion search precision isn?t set to its maximum (6)? Because, if I understand it correctly, VHQ at these higher levels does something similar to MSP.
And I have the same question concerning chroma motion. Should I rather set MSP to 5 with chroma motion or 6 without it (encoding time is similar)?
No idea. MSP=6 is an extra search that tries *different* starting points in a hope to find real motion, in case normal search would fail. In theory it has nothing to do with CM nor VHQ, except that it also takes time and improves psnr ;)

BTW, VHQ's search always includes chroma, so one might say that you're doing the same think twice if using VHQ4 and CM. At the other hand, without CM motion estimation might not find the real motion, but might do that with CM (it's always a help to have as much data as possible). In such case, CM would help VHQ by making it start at a better position. Same applies to MSP=6.

OK I'll stop guessing now. The only way to find out what's the result of messing with ME options is to try. I can only say that ME will always work, even if you choose something strange. :)

Radek

[Didée]

Originally posted by mf
Always use MSP at max and VHQ at max. The problems with VHQ>1 have long since been fixed.
Mind you, that's what I do all the time. I said it'd be interesting to know what's going on in abovementioned case.

And I am not convinced that VHQ is already carved in stone - XviD still does have a minor floating-wall problem. Plus, why is there the need at all for "cartoon" ME? ;)

Alas, I'm a little short with time for testing actually (lots of hardware fiddling, and 200~300 GB of data to shuffle around between several old <--> new HD's, & that task is to perform two times.)

- Didée

[edit] lost the posting race vs. syskin ;)

[mf]

Originally posted by Didée
Mind you, that's what I do all the time. I said it'd be interesting to know what's going on in abovementioned case.
My post was more meant at the thread starter.

[Killgore]

Originally posted by mf
Always use MSP at max and VHQ at max. The problems with VHQ>1 have long since been fixed.

Well, I'd love to, but I'm afraid I don't have enough processing power. It takes ages to do some VHQ 4 encoding on my 1GHz P3. So, I'm trying to find some compromise between quality and speed.